The present invention relates generally to a method and system of tagging unexploded ordnances, and more particularly to a method of and system for attaching a radio frequency identification (RFID) tag to a metal ordnance.
It has been shown that a RFID system can provide a means for detecting and localizing unexploded ordnances in a field environment.1 Attaching a RFID tag to an ordnance poses numerous challenges. One of ordinary skill recognizes the need for a mounted tag to withstand the physical forces associated with landing impact. Lesser forces, which may also compromise the tag's integrity, include those applied in handling, assembling, and loading. Launch of the ordnance presents yet another set of forces which a mounted tag would need to withstand. It is also desirable for the attachment itself to be rugged enough to survive the forces of landing impact, such that the tag remains associated with the ordnance.
A RFID tag will have an antenna for communication with, for example, a reader. Many ordnances, to include general purpose bombs, have an outer metal casings. Signal receipt and transmission from a tag antenna housed within a metal casing would be quite impaired. Mounting an antenna on a bomb exterior poses challenges, which include surviving impact.
Tail kits are conventionally attached to many ordnances and are chosen to provide a desired flight speed and trajectory. It would be desirable for the tag when mounted to have an insignificant or undetectable effect on ordnance aerodynamics and target penetration. It is also desirable to be able to retrofit existing ordnance inventory with a RFID tag. It would be desirable to have a tagging method which was compatible with numerous ordnances in various configurations.
Conventionally, RFID tags have been mounted to mark (MK) 52 practice bombs. The MK 52 has a dough molded body and a composite fin. The MK 52 bomb is adopted for the 500-lb MK 82 bomb and is used, for example, for practicing delivery techniques.2 FIG. 1A shows a conventional MK 52 100 with its dough body 110, composite tail assembly 120, and nose assembly 135. Conventional tag mounting protocols include cutting grooves into the aft of the tube body 125. Another similar conventional mounting protocol includes cutting grooves in each tail fin 120-1-120-4. FIG. 18 shows one of four fins 120-1 with a groove of composite 126 removed and replaced with epoxy 140. A tag 142 is set in the epoxy. In accordance with this conventional method, each fin of tail assembly 120 has a groove cut and filled with epoxy and or a tag with epoxy, not shown.
Removing equal grooves in each fin of the tail assembly 120 and filling the same with epoxy may decrease the effect of modifying the fin on the ordnance's aerodynamics. While cutting grooves in a dough or composite material may be efficient, the same method may be significantly less efficient in metal, for example steel.
Referring to FIG. 1A, yet another conventional method of mounting a tag in a MK 52 is to mount the RFID tag between the nose 135 and the body 110. Since the subject body is non-metal, electromagnetic energy may penetrate the casing to energize a passive tag. However, a passive tag mounted in a metal casing body would not receive the same needed energy transfer from a reader. The tags mounted in the MK 52s were passive.1 The nose assembly of the practice MK 52 is relatively simple and consistent across MK 52s. In contrast, the nose assemblies of any of the MK 80 series body ordnances varies considerably depending on the type of ordnance and affixing a tag into this region may not be feasible. These tag mounting methods do not readily translate into viable or practical tag mounting techniques for the metal casing and metal fins of general purpose bombs, guided ordnances, or metal casing practice bombs.
It would be desirable to have a tag mounting method and system which had minimal effect on bomb aerodynamics. It would also be desirable if the system and method were applicable to a wide range of ordnance types. And it would be desirable if metal casing bombs could be readily retrofitted with a tag mounting system and method. The mounted RFID tag must be rugged and reliable. Ruggedness is needed to withstand the launching of the ordnance and its destination impact as well as any intermediate contacts.